Low Friction Rod Persuader

ABSTRACT

Instruments are provided for shifting elongate members, such as spinal rods, with respect to coupling members of spinal fixation systems. The instruments include a low friction drive mechanism having one or more rolling elements that ride along a helical groove or track in order to transform rotational movement of a drive member into linear shifting of a reducer member that shifts the elongate member. A one-way locking mechanism may be provided to selectively prevent unwanted counter-rotation of the low friction drive mechanism. The one-way locking mechanism may include annular ratchet teeth arranged on the exterior of the drive member and a ratchet pawl located adjacent to the teeth and selectively engageable therewith.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/041,876, filed Sep. 30, 2013, which is a continuation of U.S.application Ser. No. 12/977,968, filed Dec. 23, 2010, which claims thebenefit of U.S. Provisional Application No. 61/295,625, filed Jan. 15,2010, each of which is hereby incorporated by reference in theirentirety herein.

FIELD OF THE INVENTION

This invention pertains generally to medical instruments and morespecifically to spinal implant insertion instruments for spinal fixationsystems.

BACKGROUND OF THE INVENTION

Various devices for internal fixation of bone segments in the human oranimal body are known in the art. One type of system is a pedicle screwsystem, which is sometimes used as an adjunct to spinal fusion surgery,and which provides a means of gripping a spinal segment. A conventionalpedicle screw system comprises a pedicle screw anchor and arod-receiving device or coupling member. The pedicle screw anchorincludes an externally threaded stem or shank and a head portion. Therod-receiving device couples to the head portion of the pedicle screwand receives an elongate member such as a spinal rod. Two such systemsare inserted into respective vertebrae and adjusted to distract and/orstabilize a spinal column, for instance during an operation to correct aherniated disk. The pedicle screw does not, by itself, fix the spinalsegment in place, but instead operates as an anchor point to receive therod-receiving device, which in turn receives the rod. Securing the rodto two or more vertebrae limits the position of the vertebrae withrespect to one another, allowing the associated region of the spine toheal or correcting improper positioning of the vertebrae. One goal ofsuch a system is to substantially reduce and/or prevent relative motionbetween spinal segments that are being fused.

Most pedicle screw systems are “top loading,” wherein a spinal rod ispositioned above and perpendicular to the pedicle screw anchor, and thenlowered into a channel of the rod receiving device that faces upwardfrom the pedicle screw anchor. Many pedicle screw systems include athreaded locking member that is rotatably inserted into therod-receiving device on top of the rod after the spinal rod is seatedtherein in order to fix the position of the spinal rod. Threadlesslocking members with flanges that are rotated into place to interlockwith the rod-receiving device have also been disclosed, such as in U.S.Pat. No. 7,141,051 and U.S. Patent Application No. 2007/0055235. Spinalfixation systems including locking components that requirenon-rotational linear shifting (such as along the axis of therod-receiving device) for locking thereof also are known alternatives toutilizing rotatable locking members. Such linearly locking spinalsystems are disclosed, for example, in United States Patent Application2007/0225711, as well as U.S. Provisional Application Nos. 60/784,674and 60/981,821. These systems include an anchor member (e.g., a screw orhook), a compressible inner tulip member that receives a spinal rod anda pedicle screw head snap-fit thereto, a rigid outer tulip that shiftsaxially over the inner tulip to compress the inner tulip tightly ontothe screw head, and a cap member axially inserted between portions ofthe inner and outer tulip member to compress the inner tulip about therod.

Regardless of the manner in which the locking member operates, toploading pedicle screw systems (and other top loading fixation systemssuch as hook devices) are best manipulated with an instrument capable ofgrasping the rod receiving device and “reducing” the spinal rod withinthe rod receiving device (forcing the spinal rod downward to a seatedposition within the rod-receiving device). Forces imparted on thefixation system and spinal rods by the anatomy of the patient's back,including the positioning and rotation of vertebrae that are to beconnected by the fixation system, ordinarily must be overcome tocorrectly align multiple rod-receiving devices and a spinal rod. As aconsequence, significant force must often be applied in order to shiftthe spinal rod into a fully seated position within the rod-receivingdevice, allowing the surgeon to correctly secure a locking member to thedevice and lock the spinal rod therein. Thus, an instrument that canprovide a surgeon with a mechanical advantage in shifting the spinal rodinto the rod-receiving device is of great benefit. If desired, the samedevice may also be used to insert and lock the locking member during orafter reduction of the spinal rod.

Prior art reducer instruments are often bulky, such as the devicedisclosed in U.S. Patent Application No. 2003/0225408 which has aside-mounted, lever-actuated clamping mechanism that is secured inposition by a laterally-extending rack device. Other devices, such asthe device disclosed in U.S. Patent Application No. 2009/0157125, relyon a threaded drive system which requires continual rotation of a driveportion to shift the spinal rod and may have problems with binding ofparts. The friction inherent in such threaded drive systems often makesthem less than ideal to operate. In addition, cleanability of prior artinstruments is often also a concern, since they can have a number ofmoving parts that may become clogged with blood, tissue, or othermaterials. Therefore, improved tools for reducing spinal rods andinserting locking members into rod-receiving members are desired.

SUMMARY OF THE INVENTION

Reducing instruments are provided herein that mechanically assists asurgeon in positioning a spinal rod in place over the coupling deviceand provide the surgeon with mechanical leverage to adjust the elongatemember, yoke member, and anchor member into the appropriate position forcorrecting spinal defects. In accordance with one aspect of theinvention, a low friction rod reducing instrument is provided having athreadless drive system that transfers rotational movement of a driveactuator into linear motion of a reducing member through a rollingcamming interface. For instance, rolling elements that roll through aguide track of a drive member may be coupled to the reducing member toform an interface between the two members that transfers rotationalmotion of the drive member into linear motion of the reducer member withsignificantly less friction than a threaded drive system.

A one-way locking system may also be provided in the instrument in orderto selectively prevent unwanted backward motion of the low frictiondrive mechanism. The ease of use of the helical drive system describedherein may lead to unwanted reverse rotation of the drive system due tothe reduced friction involved. In other words, after advancing one ofthe members, the low friction of the rolling drive system may tend toallow the advanced reducer member to retract back away from the advancedposition thereof when a load is applied to the instrument. For instance,the forces applied to the elongate member that resist “reducing” orrepositioning of the elongate member may be able to reverse thedirection of the instrument's reducer member unless the user of theinstrument continuously provides force to the drive mechanism.Therefore, it may be desirable to include in the instrument a one-waylocking device, such as a ratchet mechanism, to maintain the positioningof the various members of the instrument when the drive mechanism isreleased. For instance, the drive member with the helical recess mayhave a portion equipped with teeth on its exterior in an annulararrangement, with a pawl mechanism positioned adjacent the teeth inorder to prevent rotation of the drive member in a backward directionbut allow rotation of the drive member in the forward direction. In oneaspect of the invention, the one-way locking device is a ratchetmechanism that includes a set of ratchet teeth, a pawl for interactingwith the ratchet teeth, and a moveable ratchet engagement member thatholds the pawl and can be shifted between engaged and disengagedpositions.

Whereas in prior art ratchet systems a pawl binds against the teeth of aratchet mechanism to prevent backward motion and requires relief fromany load placed upon the teeth prior to pivoting the pawl out of the wayto disengage the ratchet mechanism, positioning the ratchet pawl on amoveable ratchet engagement member capable of shifting the entire pawlaway from the ratchet teeth advantageously provides the ratchetmechanism with the ability to engage and disengage even when under aheavy load.

Typically, the coupling devices of a bone fixation system will includeslits or channels for receiving the elongate member, and the reducerinstrument attaches to the exterior of the coupling device in a mannerwhich allows it to direct the elongate member into the slit or channeland then force the rod toward the end of the slit or channel to fullyreduce the elongate member within the coupling device. The instrumentmay be designed to fully reduce the elongate member into the couplingdevice prior to introduction of a locking member therein for finallocking of the elongate member within the coupling device, or may bedesigned to reduce the elongate member concurrently with introduction ofthe locking member into the coupling device.

To accomplish reduction of the elongate member prior to introduction ofthe locking member, the body of the instrument may be completelycannulated to allow the introduction of a separate locking memberinsertion instrument. Alternatively, the cap locking mechanism may beconfigured as a component of the instrument that is separate from thereducing mechanism, and may even be configured so that the cap lockingmechanism is also responsible for simultaneously reducing the rod, suchas in a device wherein the cap locking portion drives the cap downwardagainst the rod in order to shift the rod into the slit or channel ofthe coupling device. In another aspect of the invention, torque andcounter torque handles may be provided to allow the application ofincreased force to drive the spinal rod toward and into the couplingdevice.

In one aspect of the invention, the reducer instrument may have a clampmember for selectively securing the coupling device to the instrument, areducer member for shifting the elongate member into place within thecoupling device, and optionally a locking member inserter to secure alocking member to the coupling device in order to capture the elongatemember therein. One or more of the members, or a separate drive actuatormember, may be provided with a helical recess on its inner or outersurface to interact with a rolling element coupled to another member inorder to transfer rotational motion of one portion of the instrumentinto linear motion of the same portion or another portion of theinstrument. In this manner, the instrument responds to manipulation inmuch the same manner as a threaded drive system, although friction isgreatly reduced due to the presence of rolling elements instead ofcomplementary threads. The need for lubrication is thereby minimized oreliminated, and cleanability of the instrument is improved since thedrive system can be fully sealed.

The drive system may include a motor assembly, although manual operationof the apparatus will primarily be described herein. Examples of motorassemblies that could be used are an electric motor, hydraulic motor, orpneumatic motor.

The components of the reducer instrument may be generally cylindrical inshape to minimize the profile of the apparatus, reducing the size of theincision necessary for surgery and subsequently reducing the recoverytime of the patient. In alternative embodiments, the components can haveother configurations such as hexagonal prism or rectangular prismconfigurations.

In one form, the clamp member may be located concentrically within thereducer member so that shifting of the reducer member simultaneouslyshifts the elongate member and exerts an inwardly-directed force ontothe clamp member in order to tightly secure the clamp member to thecoupling device. For instance, the reducer member may be configured as asleeve that slides downward around a clamp member having multipleprongs, forcing the prongs toward one another to clamp against acoupling device.

Alternatively, the reducer member or other portions of the instrumentmay be configured so that retraction of the reducer member operates torelease the clamp member. For instance, the clamp member may beconfigured so as to be biased toward a clamped position, with elementslinked to the reducer member configured to force clamping elements ofthe clamp member apart as the reducer member shifts away from thecoupling device. In this configuration, retracting the reducer memberforces the clamp member open, releasing any coupling device locatedtherein and allowing a new coupling device to be disposed between theclamp elements of the clamp member. For instance, the clamp member maybe formed as a split sleeve with slits and a central opening sized andconfigured to receive a coupling device, and the reducer member may beconfigured as a sleeve sized to surround the clamp member and fittedwith pins that slide through the slits in the clamp member, therebycausing splaying of the clamp member at certain positions.

In one preferred form, the reducer instrument includes an elongatestationary clamp member; a rotatable drive actuator operatively coupledto the clamp member; a reducing member operatively coupled to the clampmember and drive actuator so that it is shiftable along the axis of theelongate clamp member; and optionally a cap inserter. In a preferredform, the reducing member includes a sleeve portion surrounding theclamp member, while the drive member is positioned within an axial boreof the clamp member, and has a helical recess about its outer surface.The helical recess of the drive member is sized and configured toreceive rolling elements that extend through elongate openings of theclamp member and are linked to the reducing member disposed about theouter surface of the clamp member. Elongate openings in the clamp membermay be positioned so as to allow the rolling elements to contact boththe helical recess of the drive member and the interior surface of thereducing member even though the clamp member is disposed between thetwo. In this form, rotation of the drive member guides the rollingelements along the helical recess, shifting them through the elongateopening in the clamp member and, due to their linkage to the reducingmember, causing the reducing member to shift along the exterior of theclamp member. In another preferred form, a ratchet assembly is providedin order to allow rotation of the drive member in one direction butprevent rotation of the drive member in the opposite direction unlessthe ratchet assembly is disengaged.

The instruments described herein may be adapted for use with particularcoupling devices, such as those described in U.S. Pat. No. 7,141,051(issued on Nov. 28, 2006), U.S. Patent Application 2008/0045955 (Ser.No. 11/839,843), or U.S. Patent Application 2007/0225711 (Ser. No.11/726,868), all of which applications are hereby fully incorporated byreference as if fully set forth herein. The instrument, anchor member,and coupling device may all be fully cannulated so that a wire can bepassed therethrough for minimally invasive surgical (MIS) systems. Insuch systems, a guide wire is attached to a predetermined point on thesurface of a bone, and then elements of an implant such as the couplingdevice mentioned above are passed around the guide wire so that theguide wire directs the implant elements to the predetermined point onthe bone. Similarly, the instrument for reducing an elongate member intothe coupling device also can be cannulated, i.e. contain a pathwaythrough the center of the tool so that the aforementioned guide wirethreaded through the anchor and coupling device can be threaded throughthe body of the instrument and is able to direct implantation ormanipulation of the system without interfering with the operation of thetool. The accuracy gained by use of such a guide wire reduces the amountof tissue affected by the surgical procedure and reduces recovery timefor the patient.

The reducer instrument can be made from any suitable, structurallystrong material. Preferably, the reducer instrument, especially theexterior portion is constructed of metallic materials such as stainlesssteel or other metal alloys such as titanium. Coatings, such as chromecoatings, and lubricants may also be applied in order to reduce frictionand otherwise enhance function of the instrument. The reducer instrumentapparatus also can be made from non-conductive material such as variousplastics, including polyetheretherketone (PEEK) and related compounds,in order to avoid conduction of electricity. The reducer instrument alsocan be made from ceramics that also provide non-conductivecharacteristics. Combinations of the foregoing materials also can beused that combine the properties of the said materials, i.e. metalscombined with non-conductive materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exterior perspective view of one embodiment of an elongatereducer instrument.

FIG. 2 is a perspective view of the instrument of FIG. 1 with certainexterior portions removed to reveal portions of a drive mechanism andratchet mechanism.

FIG. 3A is an exploded perspective view of the instrument portions shownin FIG. 2.

FIG. 3B is a perspective view of an alternative drive member for theinstrument shown in FIG. 3A.

FIG. 4 is an enlarged view of a head portion of the instrument shown inFIGS. 1-3.

FIG. 5 is an exploded perspective view of the ratchet subassembly of theinstrument of FIG. 1.

FIG. 6 is a perspective view of the partially assembled ratchetsubassembly of FIG. 5 with a ratchet cover removed.

FIG. 7 is a cross-sectional view of the ratchet subassembly shown inFIGS. 5 and 6.

FIG. 8 is a perspective view of the interior of the ratchet cover with aratchet arm and pawl positioned therein.

FIG. 9 is a cross-sectional view of the instrument of FIG. 1.

FIG. 10 is a magnified view of the distal portion of FIG. 9.

FIG. 11 is a magnified view of the proximal portion of FIG. 9.

DETAILED DESCRIPTION

FIG. 1 illustrates a particular embodiment of the reducer instrumentdisclosed herein. The exemplary instrument includes a central clampmember with clamping prongs 21 designed to engage a coupling device suchas a pedicle screw assembly, a reducer sleeve 10 with a head portion 5that is contoured to abut a spinal rod and shift the rod along theinstrument axis 3, and a rotatable actuator 45 configured to shift thereducer sleeve 10 axially when rotated. Rotatable actuator 45 includestwo lateral flanges 47 in order to form a T shape for easy manipulationby a surgeon. A ratchet system, which minimizes or substantiallyprevents unwanted backward rotation of the handle 45 when engaged, islocated within the instrument and hidden from view by a ratchet housing53 and a ratchet cover 58.

The reducer head portion 5 of the exemplary instrument includes areducing surface 6 formed as a semi-cylindrical notch designed to matchthe contour of the spinal rod to be reduced, and also includes a window7 to assist in visualization of the coupling member that is receivedtherein and secured by the clamping prongs 21. A bumper material (or thelike) could be positioned at the end of the head portion 5 to preventaccidental notching of the spinal rod as the head portion 5 drivesdownward and exerts force against the rod. In addition, a holdingmechanism such as a spring clip or friction fit arrangement could beincluded with the head portion to secure the spinal rod during thereduction procedure.

In use, the instrument 1 is secured to a coupling device implanted intoa vertebra by disposing the coupling device between clamping prongs 21.The actuator handle 45 is rotated to shift the reducer sleeve 10 and itsattached reducing head 5 toward the distal end 2 of the instrument 1. Asshown in FIG. 1, the reducing sleeve 10 and head 5 are in the fullyextended position, shifted to their maximal point toward the distal end2 of the tool. In this state, the reducing head 5 ensures that theclamping prongs 21 cannot splay outward, thus making the instrumentcapable of tightly securing a coupling device between the clampingprongs 21. At this point, the reducing surface 6 is also positioned sothat spinal rod contacting the reducing surface 6 would be fully seatedwithin a coupling device trapped between the clamping prongs 21.Retracting the reducing sleeve 10 causes pins 14 coupled thereto tosplay apart the clamping prongs 21, releasing the coupling device.

The actuator 45 may also be formed with a variety of different shapes aslong as the surgeon is able to rotate the actuator sufficiently to causedesired shifting of the reducer member 10. For instance, the rotatableactuator 45 may be formed in an L shape or given a cylindrical orpolygonal shape. In the exemplary instrument, a polygonal interface 60for a counter torque handle is supplied. By securing a wrench-likecounter torque handle to the interface 60, the surgeon may stabilize theposition of the instrument 1 while rotating the rotatable actuator 45.

Since the spinal rod is fully seated in the coupling device when thereducer sleeve 10 and reducer head 5 reach the positions shown in FIG.1, a locking member, such as a locking cap, may be inserted at thatpoint into the coupling device and over the spinal rod, locking thespinal rod in place. The exemplary instrument of FIG. 1 is designed tobe fully cannulated, as described below, and therefore allows for aseparate locking member insertion instrument to be introduced throughthe axial bore 49 in the rotatable actuator 45. The bore 49 leads toaxial bores through the other components of the instrument, as describedbelow. In the illustrated embodiment, the separate locking memberinsertion instrument may slide into the bore 49, although in otherembodiments the insertion instrument may be introduced in other manners,such as rotationally via a threaded drive system or a ball screw system.As the locking member reaches the coupling device trapped between theclamping prongs 21, the user will be able to see the orientation andaxial positioning of the locking member through the window 7 in thereducer head portion 5. This allows the user to manipulate the lockingmember inserter as necessary at the proximal end 4 of the instrument,such as by rotating or linearly shifting the locking member inserter asit is disposed within the reducer instrument in order to properlyposition the locking member, which can be seen through the window 7.

The axial shifting of the reducer sleeve 10 is accomplished through arolling interface between a rotatable actuator 30 linked to the actuatorhandle 45 and the internal surface of the reducer sleeve 10. Thisinterface is shielded by a cover sleeve 15, which prevents dust, dirt,and other debris from clogging the interface. This interface is betterillustrated by FIGS. 2 and 3. In FIG. 2, the instrument 1 is shown withthe cover sleeve 15 removed. In addition, several components of aratchet subassembly including a ratchet housing 53 and ratchet cover 58have been removed from the proximal portion 4 of the instrument (theportion closest to the surgeon). The ratchet system of the instrumentprevents counter-rotation of the actuator 45 and drive member 30 whenengaged, and will be described in greater detail below. The annularratchet teeth 52 exposed by removal of the ratchet cover 58 are integralto a drive member 30 that is coupled to the actuator handle 45. Thedrive member 30 is disposed concentrically within the clamp member 20,and is rotatable with respect thereto. In order to assist rotation ofthe drive member 30, two circular arrays of ball bearings 62 and 64 areprovided. The ball bearings are disposed on both sides of an annularflange 65 protruding from the drive member 30. The lower bearing array64 permits smooth rotation between the drive member 30 and the proximalend of the clamp member 20. The upper bearing array 62 facilitatessmooth rotation between the drive member 30 and a ratchet housing thatis normally disposed about the ratchet teeth 52. The drive member alsoincludes a helical groove 35, which can be seen in FIG. 2 through anelongate opening or slit 27 in the clamp member 20.

The reducer sleeve 10 is disposed about the exterior of the clamp member20. The reducer sleeve 10 is operatively coupled to the rotatable drivemember 30 through rolling elements 36 which in the illustratedembodiment are spherical elements 36. These spherical elements arepartially disposed in circular openings 12 in the reducer sleeve 10, andextend inward through the slit 27 in the clamp member and into thehelical groove 35 of the rotatable drive member 30. Thus, as therotatable drive member 30 is rotated the spherical elements will travelalong the track created by the helical groove 35. Since the sphericalelements 36 are confined to the axial slits 27 in the clamp member,rotation of the drive member 30 causes the spherical elements 36 toshift axially along the slit 27, which acts as a vertical guide track asthe spherical elements 36 ride through the helical track formed by theannular groove 35. Being partially disposed in the circular openings 12of the reducing sleeve 10, vertical movement of the rolling sphericalelements 36 in turn causes axial shifting of the sleeve 10. Rotation ofthe handle 45 and associated drive member 30 in a first direction causesshifting of the spherical elements 36 and associated sleeve 10 towardthe distal end of the instrument 2, while rotating the handle 45 in theopposite direction causes shifting of the spherical elements 36 andsleeve 10 toward the proximal end of the instrument, retracting thereducing sleeve 10 and reducer head 5. The continuous rolling of thespherical elements 36 as they interact with the helical guide track 35of the drive member 30, vertical guide track 27 of the stationary clampmember 20, and openings 12 of the reducer member 10 minimizes frictionin the system and thereby allows the surgeon to easily and quicklyadvance the reducer member 10.

The primary components of the aforementioned drive coupling are shown inFIG. 3A in a disassembled state. In the illustrated form the drivemember 30, clamping member 20, reducer sleeve 10, and reducer headportion 5, are all hollow generally cylindrical elements that arepositioned relative to one another so as to share a common axis. Thedrive member 30 includes an actuator handle 45, an annular array ofratchet teeth 52, a bearing flange 65, and a helical recess 35 thatforms part of a ball screw arrangement. An opening 49 at the top of theactuator handle 45 leads to an axial bore 31 running the entire lengthof the drive member 30. The lower portion of the drive member 30, whichincludes the helical recess 35, is placed within a bore 29 at the top ofthe clamp member 20. The lower part of the drive member therefore restsin a slightly widened portion of the clamp member 20, so that thehelical recess 35 of the drive member 30 is positioned behind the slit27 and openings 26 of the clamp member 20. When the drive member 30 ispositioned within the bore 29 of the clamp member 20, the bearing flange65 rests slightly above the top end of the clamp member 20. This allowsfor an array of ball bearings 64 (FIG. 2) to be positioned betweenflange 65 and the top of the clamp member 20. These ball bearingsfacilitate rotation between the drive member 30 and the clamp member 20.

The clamp member 20, like the drive member 30, is relatively cylindricalin shape and hollow so that a bore 29 runs axially through the entiretyof the member. A series of openings 26 and 28 are provided in the clampmember in order to reduce the overall weight of the instrument. Theclamp member 20 includes at its distal end two prongs 21 formed by aforking of the body of the clamp member 20. A gap 23 is formed betweenthe two prongs 21 which allows the prongs to resiliently deflectoutwardly an inwardly. A circular gap enlargement 24 at the top of thegap 23 reduces the stress on the clamp member 20 when the prongs 21 aresplayed apart. The prongs 21 may be equipped with holding pegs 22 orother features that are shaped to mate with the exterior of a couplingdevice that is to be secured and manipulated by the instrument. Theclamp member 20 is received in an axial bore 11 of the reducer sleeve10.

The reducing sleeve 10 includes circular openings 12 designed to holdspherical rolling elements. These spherical rolling elements are alsosized and configured to fit within the helical recess 35 of the drivemember 30, and fit within the slit 27 of the clamping member 20. Thespherical rolling elements thus link the drive member 30 and the sleeve10 through the axial slit 27 of the clamp member 20. At its oppositeend, the sleeve 10 includes openings 13 spaced diametrically oppositeone another and each sized to receive a deflection pin 14. Thedeflection pins 14 are also sized to be received in openings 8 of thereducer head portion 5. Thus, the pins 14 are capable of securing thereducer head portion 5 to the reducer sleeve 10 when the openings 8 andthe head portion 5 and the openings 13 in the sleeve portion 10 arealigned with one another. The deflection pins 14 also serve tomanipulate the clamping mechanism of the instrument. As the drive member30 is rotated in a reverse direction to retract the reducer sleeve 10,the sleeve will shift towards the upper end (proximal end) of theinstrument. As the pins 14 move along with the sleeve 10, they slidelinearly through the gap 23 between the clamping prongs 21. The prongs21 and gap 23 between them may be configured as shown so that the gap 23narrows towards its top and the pins 14 may be sized so that as theyreach this narrowed portion of the gap 23, the clamping prongs 21 aresplayed slightly outward. Conversely, rotation of the drive member 30 inthe opposite, forward direction shifts the reducer sleeve 10 toward thedistal end of the instrument, so that the deflection pins 14 arepositioned in a wider portion of the gap 23 and no longer cause splayingof the clamping prongs 21. Further, the presence of the sleeve 10 aboutthe exterior of the clamping prongs 21 assures that the prongs cannotdeflect outward, thus tightly clamping any coupling device trappedbetween the prongs 21.

An alternative drive member 30 a is illustrated in FIG. 3B. This drivemember has a helical groove 35 a with a varying pitch, so that thevertical distance traveled by the rolling element 36 a disposed in thegroove 35 a with a set degree of rotation of the drive member 30 achanges depending on the position of the rolling element 36 a. As aresult, a given degree of rotation of the drive member results in adifferent amount of linear shifting of the reducer member 10 dependingon the positioning of the reducer member. In the illustrated embodiment,the pitch of the groove 35 a is shallower toward the distal end of thedrive member so that as the reducer sleeve approaches its fully extendedposition the reducer sleeve advances at a decreased rate, allowing thesurgeon to more easily make fine adjustments at the end of the reductionprocedure. The more pronounced pitch at the top end of the helicalgroove, on the other hand, allows the reducer member 10 to be advancedquickly to a position where it is close to engaging the rod. While themore pronounced pitch in this section of the groove 35 a does notprovide as great a mechanical advantage to the surgeon, the force thatthe instrument must exert to shift a spinal rod is usually much lowerfurther from the seated position, and increase as the rod becomes morefully reduced. Therefore, the varying pitch of the helical groove 35 aillustrated in FIG. 3B allows the instrument to be rapidly adjusted atpositions or distances where it is not necessary for the instrument togenerate large amounts of force.

FIG. 4 shows the reducer head portion 5 of the reducer instrument. Thishead portion 5 is designed to abut a spinal rod or other elongate memberand drive that elongate member into a coupling device that is heldbetween the two prongs 21 of the clamp member 20. As discussed above,the head portion 5 includes a reducing surface 6 at one end contoured toreceive the spinal rod or other elongate member. In the illustratedembodiment, this reducing surface is formed as a concave semi-circle ora semi-cylindrical surface. It is possible, however, for the reducingsurface to have a variety of shapes and sizes. The opposite end of thehead portion 5 is designed to be secured to the reducing sleeve 10. Thedeflection pins 14 are positioned through openings in the reducingsleeve 10 and also in the circular openings 8 of the reducer headportion 5. The circular openings 8 are positioned within tabs 8 a or asimilar structure that may slide into or over the reducer sleeve 10. Thereducer head portion 5 also includes an axial bore 9 that is shaped andsized to receive a coupling device held between the clamping prongs 21.A window 7 is provided in each side of the reducer head portion 5 inorder to allow the user to see the coupling device that is held by theinstrument even when the reducer head portion 5 is in the fully extendedposition. In order to allow for a visualization of the coupling device,the clamping member prongs 21 are arranged in either side of the window7, so that the gap 23 between the prongs 21 is aligned with the window7.

Movement of the reducer sleeve in the illustrated embodiment isregulated by a ratchet mechanism, which may be engaged in order toprevent retrograde motion of the reducer sleeve and reducer headportion. When the ratchet mechanism is engaged, it allows the drivemember 30 to be rotated in only one of a clockwise and counterclockwisedirection, and prevents rotation in the opposite direction. Reverserotation of the drive member 30 is prevented by the interaction of theannular arrangement of the ratchet teeth 52 of the drive member 30 and apawl mechanism coupled to the clamping member 20 in which the drivemember 30 is located (see FIGS. 2 and 3). The portions of the ratchetmechanism that are coupled to the clamping member 20 include a ratchethousing 53, a ratchet arm 54, and a ratchet pawl 55. The ratchet arm 54and ratchet pawl 55 are held within the ratchet housing 53 as explainedbelow. An annular ratchet cover 58 is designed to surround the upperportion of the ratchet housing 53 to cover the elements of the ratchetmechanism. Furthermore, rotation of the ratchet cover 58 serves toengage and disengage the ratchet mechanism by selectively forcing theratchet arm and associated pawl toward the ratchet teeth.

As seen in FIGS. 5 and 6, the ratchet housing 53 is disposed about theannular ratchet 52 in the assembled instrument, and rests above theannular flange 65 of the drive member 30. An array of ball bearings 62is disposed above the annular flange 65 and below a surface of thebearing housing 53. The ball bearing array 62 may be held in place by acircular bearing retainer 61. When the ratchet housing 53 is fixed withrespect to the clamp member 20, such as by welding the two componentstogether, the bearing array 62 facilitates rotation between the drivemember 30 carrying the annular ratchet teeth 52 and the ratchet housing53 that carries the ratchet arm 54 and ratchet pawl 55.

The bearing housing 53 includes a base member 72 that rests above theannular flange 65 of the drive member 30 and the bearing array 62designed to facilitate rotation between the drive member 30 and theratchet housing 53. Extending downward from the base member 72 is anannular wall 71. This annular wall 71 covers the bearing arrays 62 and64 that are adjacent to annular flange 65 of the drive member 30, andthe annular wall 71 may be welded to the clamp member 20 (see FIGS. 2-3)in order to seal off the bearing arrays 62 and 64. The portion of theratchet housing 53 above the base member 72 forms a c-shaped wall 73,which is essentially an annular wall with a gap 75 disposed therein. Gap75 provides space for the ratchet arm 54 to be situated therein,adjacent the annular ratchet teeth 52 of the drive member 30. Theratchet arm 54 is connected to a post member 57 that is taller than theratchet arm and interacts with an upper surface of the interior of theratchet cover 58. The post member and the configuration of the c-shapedwall 73 allow the ratchet arm 54 to pivot toward and away from thecenter of the ratchet housing 53, in which the annular ratchet teeth 52are disposed when instrument is assembled. The ratchet cover 58 isdisposed around the c-shaped wall 73 of the ratchet housing 53 and alsoserves to contain the ratchet arm 54 and associated ratchet pawl 55. Theouter wall of the ratchet cover limits the movement of the ratchet arm54 away from the annular teeth 52.

The ratchet housing 53, ratchet arm 54, ratchet pawl 55, and post 57 areshown in FIG. 6 in position relative to the drive member 30 and theannular array of ratchet teeth 52 provided thereon in order to form themajority of the ratchet assembly. The ratchet cover 58 slides downaround the top end of the drive member 30 and around the c-shaped wall73 of the ratchet housing 53 in order to complete the ratchet assembly.In its final position, the ratchet cover 58 sits atop the base member 72of the ratchet housing 53 and may be rotated relative to the ratchethousing 53 in order to engage and disengage the ratchet mechanism. Inparticular, as will be explained below, rotation of the ratchet cover 58in one direction holds the ratchet arm 54 against the annular teeth 52so that the ratchet pawl 55 is forced to engage the teeth 52 and allowthem to pass in only one direction, allowing the drive member 30 torotate in a first direction but preventing the drive member 30 fromrotation in a second opposite direction. When the ratchet cover 58 isrotated in the opposite direction to a second position, the ratchet arm54 is allowed to fall away from the ratchet teeth 52, so that the pawl55 no longer is tightly engaged to the annular ratchet teeth 52 andallowed them to pass when the drive member 30 is rotated in either aclockwise or counterclockwise direction.

Ordinarily, a pivotable ratchet pawl is disengaged by simply pivotingthe contact points away from the ratchet teeth, allowing the teeth topass unhindered by the disengaged pawl. However, since the pawl preventsbackward movement of the ratchet teeth by binding against the rearsurfaces of the teeth, the ratchet teeth must normally be advanced by aslight amount in order to relieve any binding between the pawl and theteeth, providing the pawl with room to pivot out of the way. In otherwords, the load placed on the ratchet mechanism by the forces which theratchet mechanism is designed to resist must ordinarily be relievedbefore the ratchet pawl can be pivoted away from the ratchet teeth todisengage the ratchet mechanism. In the instrument shown in FIGS. 1-11,however, this is problematic because it is of great advantage for theratchet mechanism to be able to hold the reducer member in a fullyadvanced state, and further advancement to disengage the ratchetmechanism would ordinarily be impossible at that point. However, theratchet mechanism shown in FIGS. 5 and 6 solves this problem by mountingthe ratchet pawl 55 to a moveable arm 54 so that the entire pawl can beshifted away from the array of ratchet teeth 52 to disengage the ratchetmechanism instead of simply pivoting the pawl mechanism. Thus, bymounting the pawl 55 to a moveable ratchet arm 54, the ratchet mechanismhas the ability to engage and disengage without further advancement ofthe reducer member even when under a heavy load. The reducer sleeve 10of the instrument may therefore be released directly from a fullyextended position without exerting additional forward force on thereducer sleeve that could potentially damage the spinal rod that it isreducing.

FIGS. 7 and 8 depict the ratchet cover 58 from below, with the ratchetarm 54 and the ratchet pawl 55 in place and in an engaged position. Thedrive member 30 with the associated array of the annular ratchet teeth52 (see FIG. 6) normally would be disposed through the opening 80 in theratchet cover 58. The ratchet arm 50 and ratchet pawl 55 are designed torest adjacent to the ratchet teeth. The ratchet cover 58 includes anupper wall 76 and an annular outer wall 81. The thickness of the outerwall 81 varies so that rotation of the ratchet cover 58 engages anddisengages the ratchet arm 54 with the annular teeth of the drivemember. Where the outer annular wall 81 is thinnest, a recess or space78 is created that allows the ratchet arm 54 to pivot outwardly and awayfrom the annular teeth at the center of the ratchet mechanism. As theratchet cover 58 is rotated into an engagement position, a shoulder 79of the inner wall 75 begins to engage the pivotable ratchet arm 54 andforces the arm inward so that the ratchet pawl 55 cradled by the ratchetarm 54 abuts the ratchet teeth. The ratchet pawl is allowed to swing inone direction (clockwise as viewed from below) to allow the ratchetteeth to pass, but attempts to rotate the ratchet teeth in the oppositedirection are prevented to the interaction of the ratchet pawl 55 and anabutment surface 85 created by the shape of the ratchet arm 54 thatholds the pawl. A ratchet spring 56 disposed within the arm 54 biasesthe pawl 55 into a position wherein the pawl engages the ratchet teeth,but allows the pawl to pivot outward into a notch 86 in the arm 54 inorder to allow the ratchet teeth to pass by. It will be understood thatwhen the ratchet cover 58 is positioned so that the space 78 formed bythe thinning of the outer wall is adjacent the free end 87 of theratchet arm 54, rotation of the ratchet teeth in a direction that forcesthe pawl 55 against the abutment surface 85 of the arm 54 will simplycause the entire arm 54 to pivot outwardly, shifting the free end 87 ofthe arm out into the open space 78 and letting the ratchet teeth pass bythe pawl unobstructed. As previously mentioned, without the moveableratchet arm 54, release of the ratchet mechanism would require rotationof the ratchet teeth 52 in a counterclockwise direction (as viewed inFIG. 7) until the pawl 55 had sufficient room to pivot clockwise out ofthe way of the teeth. By mounting the pawl 55 in a ratchet arm 54 thatis itself pivotable or otherwise moveable, the ratchet mechanism may bereleased from any given point, even when a significant force biases theratchet teeth 52 in a clockwise direction.

A post slot 77 (FIG. 8) forms an arc in the upper wall 76 of the ratchetcover 58 and directs the post 57 to slide therein to shift the positionof the arm 54 as the ratchet cover 58 rotates from an engagementposition to a disengagement position and back again. In other words, theshape and direction of the slot 77 cause shifting of the post 57 as theratchet cover 58 is rotated, which in turn causes the ratchet arm 54 topivot toward and away from the ratchet teeth. Alternatively, the arm maybe configured to be shifted solely by forces exerted by rotation of theratchet teeth that push the arm outward.

FIGS. 9 through 11 show cross sectional views of the instrument ofFIG. 1. FIG. 9 is a cross section view of the entire reducer instrumentof FIG. 1 grasping a representative coupling device 90 and reducing aspinal rod 95 into the device 90. The illustrated coupling device 90includes a shank or screw portion 93 that is driven into a boney surface97 of a vertebra. The device 90 alternatively may be secured by othermeans to vertebra, such as by a hook or a wire. The clamp member prongs21 of the instrument surround the coupling device 90 on both sides, andholding pegs 22 interface with complimentary openings or indentations oneither side of the coupling device 90.

As shown in the magnified view of FIG. 10, the reducer head portion 5 isdisposed about the exterior of the clamping prongs 21. As best seen inFIG. 10, the reducer head 5 lies below the reducer sleeve 10, as coupledthereto by pin 14. The reducer head portion 5 fits tightly around theclamp prongs 21 holding the coupling device 90 to the lower portion ofthe prongs 21. However, there is adequate space 77 between the clampingprongs 21 and the reducer sleeve 10 and/or reducer head portion 5 towardthe top of the clamp members 21 that when the reducer sleeve 10 andreducer head portion 5 are retracted above the shoulder portion 75 ofthe clamp prongs 21 they do not interfere with lateral splaying of theclamping prongs 21. This lateral splaying allows the coupling device 90to be received between and removed from the clamping prongs 21. Thereducer sleeve 10 and reducer head 5 shift downward to abut the shoulderportion of the clamping prongs 21 and then slide snugly around theexterior of the clamping prongs, preventing any outward splaying of theclamping prongs 21 and holding the prongs tightly to the coupling device90. In order to release the coupling device 90, the reducer head portion5 and reducer sleeve 10 are retracted, sliding upward past the clampingprong shoulder portion to permit outward splaying of the clamping prongs21. Simultaneously, the pin 14 holding the reducer head portion 5 to thereducer sleeve 10 shifts upward and will abut the ramp portion 79 formedby the narrowing of the gap 23 between the clamping prongs 21. Abutmentof the pin 14 against the ramp portion will force the clamping prongsapart, releasing the coupling device 90.

FIG. 11 is a magnified cross sectional view of the ratchet mechanism andthe drive mechanism of the reducer instrument. The drive actuator handle45 is fixed to the drive member 30, with the drive member 30 isrotatably inserted into the clamp member 20. The annular flange 65 ofthe drive member 30 rests above the top end of the clamping member 20with a bearing array 61 disposed between the annular flange 65 andclamping member 20 in order to facilitate rotation between the two. Thedrive member 30 is coupled to the reducer sleeve 10 disposed about theexterior of the clamping member 20 by force rolling spherical element 36that are partially disposed in a helical groove 35 of the drive member30 and openings 12 of the reducer sleeve 10. A vertical slit 27 in theclamping member 20 allows the rolling spherical elements 36 to contactboth the drive members 30 and the reducer sleeve 10 despite the clampingmember 20 being disposed between the two. The helical groove 35 of thedrive member may have a varied pitch so that a given degree of rotationof the drive member results in a different amount of linear shifting ofthe reducer member 10 depending on the positioning of the reducermember. For instance, the pitch of the groove 35 may become shallowertoward the distal end of the drive member so that as the reducer sleeveapproaches its fully extended position the reducer sleeve advances moreslowly and provides the surgeon with a greater mechanical advantage,allowing the surgeon to more easily make fine adjustments at the end ofthe reducing procedure.

A cover sleeve 15 is fixed to the clamping member 20 and covers theportion of the reducer sleeve 10 containing the rolling sphericalelements 36. This protects the rolling spherical elements and othercomponents of the drive mechanism from dirt and debris. The cover sleeve15 may be secured to the clamping member 20 by welding, adhesive, orother means.

As discussed previously, rotation of the drive member 30 may beselectively limited by a ratchet mechanism. FIG. 11 also illustrates theratchet mechanism shown in FIGS. 5-8. The ratchet housing 53 is mountedto the upper end of the clamping member 20 and prevents the drive member30 from moving vertically due to interference between the annular flange65 of the drive member and the inner surface of the housing 53. An arrayof ball bearings 63 is disposed between the two in order to facilitaterotation of the drive member 30. The upper wall 73 of the ratchethousing 53 is c-shaped to accommodate a ratchet arm 54 on one side ofthe instrument. A rotatable ratchet cover 58 is disposed about the upperc-shaped wall 73 of the ratchet housing 53, and maintains the ratchetarm 54 in position. Selective rotation of the ratchet cover 58 engagesand disengages the ratchet arm 54 with teeth 55 disposed about the drivemember 30, as previously discussed.

In order to lock the elongate member to the coupling member 90 once theinstrument has been used to reduce the elongate member, a locking memberinserter may be provided. Since the full interior of the illustratedinstrument is cannulated, as best shown in FIG. 9, the locking memberinserter may be inserted through the opening 49 at the proximal end ofthe instrument and downward through the axial through bore formedthrough the instrument.

One exemplary locking member inserter 100 is illustrated in FIG. 11, andincludes an elongate body 101 long enough to reach the coupling device90 through the entire length of the cannulated interior of the reducerinstrument 1. The locking member inserter 100 also has a head portion103 that holds a locking member 96 in position in order to introduce thelocking member 96 into the coupling device 90. The locking memberinserter may contain a handle to assist the surgeon in locking thelocking member. For instance, if the locking member must be rotated to alocked position within the coupling device 90, a T-shaped handle such asthe illustrated handle 102 may be provided at the end of the inserter toprovide the surgeon with a mechanical advantage for rotating theinserter 100 and locking member 96. In addition, in some instances theinserter 100 will be provided with wings 104 or other structures toguide the alignment of the inserter and locking member 96. The wings 104would be designed to interact with structures (such as guide channels)in the interior of the reducer instrument 1 to align the locking member96 properly with the coupling device 90 held by the reducer instrument1.

It is intended for the following claims to cover these and any otherdepartures from the disclosed embodiment which fall within the truespirit of the invention.

What is claimed is:
 1. A reducer instrument for a spinal rod, thereducer instrument comprising: a clamp member having a distal portionconfigured for being oriented about a coupling device for the spinalrod; a reducer member configured to engage the spinal rod; a drivemember rotatably relative to both the clamp member and the reducermember; and a rotary coupling between the drive member and the reducermember including a rolling ball element held by the reducer member and ahelical groove of the drive member in which the rolling ball element isreceived to travel therein to convert an input rotary drive forceapplied to the drive member to translatory motion of the reducer memberalong the clamp member.
 2. The reducer instrument of claim 1 wherein theclamp member has an axial slit, and rotating the drive member causes therolling ball element to travel axially along the axial slit of the clampmember as the rolling ball element travels in the helical groove of thedrive member.
 3. The reducer instrument of claim 1 wherein the drivemember and the clamp member are configured so that the drive member andthe clamp member do not translate relative to each other as the drivemember is rotated.
 4. The reducer instrument of claim 1 wherein theclamp member has a bore, and the drive member has a portion includingthe helical groove thereof that is configured to be received and rotatedin the bore of the clamp member.
 5. The reducer instrument of claim 1wherein the drive member and the clamp member include coaxial throughbores for allowing a locking member to be advanced through the throughbore of the drive member and then through the through bore of theclamping member and into the coupling device for locking the spinal rodtherein.
 6. The reducer instrument of claim 1 wherein the rotarycoupling is configured to allow either the drive member to be rotated ina spinal rod reducing rotary direction causing the reducer member totranslate in a distal direction along the clamp member away from thedrive member for reducing a spinal rod into the coupling device, or thedrive member to be rotated in an opposite rotary direction to the spinalrod reducing rotary direction causing the reducer member to translate ina proximal direction along the clamp member toward the drive member. 7.The reducer instrument of claim 6 including a one-way lock between theclamp member and the drive member and being shiftable between anoperative configuration that allows the drive member to be rotated inthe spinal rod reducing rotary direction and keeps the reducer memberfrom translating in the proximal direction, and an inoperativeconfiguration that allows the drive member to be rotated in the oppositerotary direction to allow the reducer member to translate in theproximal direction.
 8. The reducer instrument of claim 7 wherein theone-way lock includes ratchet teeth of the drive member and a pawlmechanism coupled to the clamp member, the pawl mechanism including apawl whereby shifting the one-way locking mechanism to the inoperativeconfiguration allows the pawl to pivot away from the ratchet teethwithout requiring initial rotation of the drive member in the spinal rodreducing rotary direction.